1. Field of the Invention
The invention relates to a method and a device for determining the alignment of line formations of areal, in particular, longitudinally moved webs of a structural formed body. In the method for determining the alignment of line formations in areal webs of a structural formed body such as textiles, fleece, paper, braided wire or plastic material etc., a detector views a surface portion of the structural formed body, which is illuminated by a radiation source, by means of a plurality of radiation-sensitive sensors and a computer determines based on the respectively measured local radiation intensities measured by the sensors, with consideration of the position of the sensors relative to one another, the line formations and their alignment in the structural formed body. The device for determining the alignment of line formations of areal, web-shaped structural formed bodies such as textiles, fleece, paper, braided wire or plastic material etc., has a radiation source which directs radiation onto the surface of the structural formed body and a detector which faces the irradiated surface portion and has a plurality of radiation-sensitive sensors arranged in fixed spacing to one another. A computer for processing/evaluating the measured values of the sensor is connected in a signal-transmitting manner to the detector.
2. Description of the Related Art
The alignment of line formations of areal webs of a structural formed body can deviate from the ideal image upon manufacture of the structural webs. For quality assurance, information of the actual alignment of the line formations as precisely as possible is required in order to be able to correct, for example, in subsequent machining steps, possibly occurring deviations from the ideal image, for example, warpage within the textile web.
From German patent document DE 1 635 266 a method for measuring the weft yarn position of moving textile webs by a light source directed onto the textile web and a measuring device, which comprises at least one photoelectric cell affected by the light source, are known. The electrical voltage emitted by the photoelectric cell serves as a signal. The known method provides for an automatic following of the respective position of the weft yarn by the measuring device until an extreme of the signal(s) emitted by the photoelectric cell(s) results. For determining the angular deviation of the weft yarn, the deviation of the measuring device position resulting in the extreme signal value from the normal position is measured. In this measuring principle, a suitable optical device detects a linear surface element of an illuminated textile surface by a photoelectric cell, but only locally in a measuring area detectable by the optical device. In order to obtain information in regard to the alignment of the line formations across the entire web width, several such measuring devices must be arranged adjacent to one another.
In order to be able to detect the entire width of the textile length and to keep the constructive expenditure as low as possible, the German patent document 28 50 804 C2 suggests to arrange on the left and the right half of the web surface one or more sensor heads, respectively, and to move them symmetrically to the web center in opposite directions wherein the sensing signals of both halves are to be correlated with one another. The evaluation/processing of the measuring signals, which are obtained by a slot-wise viewing of the surface by optical lens systems, requires however a longer period of time. Especially with quickly moving webs and quickly and greatly changing warpage the measurements across the web width relative to one another can no longer be correlated with one another.
The German patent document 36 33 439 C2 discloses a detector arrangement with aperture slot, optical lens systems and photoelectric cells which are rotated back and forth by a step motor. In an alternative to the rotatable arrangement of the components a stationary detector arrangement with a plurality of light-sensitive sensors is suggested wherein the use of a CCD camera (charged coupled device) is suggested. In this CCD camera the light-sensitive sensors are arranged in a stationary row. A computer performs a virtual rotation of the optical system, instead of the mechanical rotation performed by the step motor, by means of evaluating individual points of the linear area of the textile with the CCD row.
In German patent document 37 17 305 C1 it is suggested to view a slot-shaped portion of the web for measuring the weft yarn or stitch row position (warpage angle) in continuously conveyed textile webs by transillumination or surface illumination methods, wherein by means of the CCD rows the brightness values within the slot-shaped portion are divided into two brightness steps (light, dark). From these digital brightness values of the CCD sensors within the measured slot-shaped portion those sections are determined within which the brightness values can be continuously coordinated with a brightness step in order to thus determine the warpage angle of the weft. The slot-shaped portion is positioned at a fixed angle to the conveying direction of the textile web. Despite the use of two CCD rows as photo sensors, the known device cannot provide a satisfactory precision in the determination of the alignment and the detection of warpage, especially for structural formed bodies with complex line formations such as tightly woven textiles.
European patent document 0 741 290 A2 discloses a method for detecting the warpage angle of continuously moving textile webs wherein the measurement across the entire width is supposedly made possible with CCD sensors in that by means of a single stationery image-producing device a real image across the width of the web is detected. The sampled image of the CCD measuring signals is saved in the form of rectangular subsections. A computer evaluates/processes the saved data with transformation algorithms, and this supposedly allows a characterization of the yarn directions across the entire textile web with. The known method can determine yarn warpage only unsatisfactorily for complex textiles even when using powerful computers.
It is an object of the present invention to provided a technically new method of the aforementioned kind and a new device in order to provide with minimal constructive expenditure a precise and fast determination of the alignment of line formations in web-shaped structural formed bodies.
In accordance with the method of the present invention, this is achieved in that the radiation source and the detector are arranged so that they can be reciprocated together and synchronously across the width of the structural formed body wherein at least at one transverse position above the areal structural formed body the local structural image is detected. The device according to the invention is characterized in that the radiation source and the detector are arranged so that they can be reciprocated together and synchronously across the width of the structural formed body.
According to the invention, it is suggested that the radiation source irradiating the structural formed body and the detector comprising a plurality of radiation-sensitive sensors are reciprocated together and synchronously across the width of the structural formed body for determining the alignment of line formations. When doing so, the local structural image of the formed body is detected at least at one transverse position above the areal web by short-time measurement within a microsecond range. It is possible to take local momentary images of the web surface at any desired predetermined transverse position without interrupting the transverse movement. The alignment of the local line formation in the viewed surface area portion is determined by the computer as a function of the local radiation intensity measured by the individual sensors. A line structure can be deduced, for example, from similar measured values of neighboring sensors. Expediently, the sensors are arranged in a matrix within a plane wherein any kind of line formation can be detected in the matrix plane. The detector and the radiation source can be arranged on the same side of the structural web wherein the sensors detect the reflected radiation of the irradiated surface. An arrangement of the detector and the radiation source on opposite sides of the structural areal web is especially advantageous wherein the structural formed body is penetrated by the radiation. For the determination of the alignment of the line formations, the web to be examined is transported between the detector and the radiation source.
The determination of the alignment of the line formations is carried out with the inventive measures independent of the transport speed of the examined structural web and can be carried out even when the structural formed body is stationary.
In a preferred embodiment of the invention an areal photo transducer with photo sensors arranged in a matrix, such as a CCD matrix, is used as a detector and a light source is used as a radiation source which emits light in the visible, infrared or ultraviolet wave range. In the alternative, it is suggested to carry out an x-ray irradiation of the structural formed body and to view the irradiated surface portion with a corresponding detector having a sensor matrix that is sensitive to x-ray radiation. This method is advantageous in particular when viewing and monitoring materials impermeable to light.
By taking into account the traversing speed of the detector and the radiation source, the computer correlates advantageously the transverse positions of the detector and the radiation source at each measuring location with the respective structural image that has been determined by the measured information. By being able to measure without stopping, it is thus possible to perform a measurement at high traversing speed and high transport speed of the areal web at any desired transverse position in order to achieve a gap-free structural image across the entire width of the areal web with high evaluation speed. Expediently, for one traversing path across the web, multiple measurements are performed at, if needed, predetermined transverse positions wherein deviations from the ideal image of the line formation are easily detected. Upon return movement of the detector, measurements at transverse positions are performed which are located between the measuring locations of the initial movement across the web.
In comparison to the prior art, a higher precision can be achieved and, moreover, any selected transverse position across the web can be measured because of the synchronous movement of the radiation source and the detector in the transverse direction of the web-shaped structural formed body. The measurements are carried out essentially independently of the movement velocity of the web, and the constructive expenditure is reduced by using a single detector. For great web widths it is however possible to use two or more detectors with corresponding radiation sources, for example, illumination sources, so that in this manner the measuring times can be shortened.
Moreover, from the structural image according to the measured signals of the radiation-sensitive sensors, especially when they are arranged in a matrix, information in regard to the line density of the structural formed body can be deduced as well as characteristic data of the structure.
When using a CCD camera for determining the alignment of the line formation, an adjustable flash is preferably used as a light source which can be adjusted with respect to intensity and illumination time. It moves with the detector in the traversing direction. The short illumination times in a microsecond range, which are sufficient for producing the local structural image, can however also be achieved by permanent light sources by using the shutter of the camera for varying the illumination times.
The radiation source and the detector can be secured on a traversing guide in a slidable manner and are guided by a suitable step drive together and simultaneously along the traversing guide. The traversing guide can be formed by rails on a measuring frame. In an arrangement of the radiation source and of the detector on opposite sides of the structural formed body two parallel rails are provided on which the radiation source and the detector are guided by means of a respective carriage. The structural formed body to be examined is guided between the rails.
The step drive for the carriages of the radiation source and the detector is controlled by the computer wherein the traversing speed and the frequency of structural image taken across the web can be adjusted according to the type of structural formed body to be examined or also according to other parameters. For example, when detecting warpage relative to a nominal alignment of the line formations the traversing speed can be changed by the computer in order to be able to obtain information in regard to the structural image more quickly by simultaneously adapting the measurements per traversing stroke. In particular, upon detecting deviations in the predetermined structural alignment, the traversing stroke or path can be shortened and the number of measurements performed during the traversing movement can be reduced. An adjustable device for limiting the traversing movement can, for example, detect the edge of the structural formed body or can be arranged at a suitable transverse position in order to send a signal for reversing the traversing movement to the computer. Also, by arranging such limitation devices, such as, for example, mirrors in the case of optical CCD systems, the correlation of the measurements and of the detected structural images of respective surface portions can be synchronized with the transverse position.